FIGS. 9(a) and 9(b) show a clip disclosed in Patent Document 1. The clip 10 comprises a grommet 12 provided with a base portion (corresponding to a projecting portion in the present application) 20 abutting against a periphery of a first attachment hole 34 bored in a member 30, and a trunk portion (corresponding to the leg portions of the present application) 22 diametrically expandably extending from the base portion, and formed by a plurality of trunk-portion formation pieces 52 inserted into the first attachment hole 34 and a second attachment hole 36 bored in a member 32; and a pin (corresponding to the shaft member in the present application) 14 provided with a head portion 24, and a shaft portion 26 extending from the head portion, and inserted to an inside of the trunk portion from a through hole of the base portion 20 to diametrically expand the trunk-portion formation pieces 52 so as to push the trunk-portion formation pieces against a hole wall side of the second attachment hole 36. The aforementioned clip 10 can switch between a lock position where the shaft member 14 is pushed into the grommet 12 for the predetermined amount to diametrically expand the trunk-portion formation pieces 52 in a state wherein engagement convex portions (corresponding to a leg-side convex portion in the present application) 54 provided on a trunk-portion formation piece side as shown in FIG. 9(a) are engaged with tip-side engagement concave portions (corresponding to a shaft-side convex portion of the present application) 40 provided on a shaft portion side; and an unlock position where when the shaft member 14 is further pushed in to the maximum degree, the engagement convex portions 54 release the engagement as shown in FIG. 9(b), and fall into head-portion-side engagement concave portions 44 provided on the shaft portion side for engagement so as to return the trunk-portion formation pieces 52 to the original condition.
Also, in the Patent Document 1, in order to obtain excellent workability when the pin 14 is returned to an upward position which is reusable relative to the grommet 12 from the condition of FIG. 9(b), the engagement convex portions 54 include convex-portion wall faces 54A inclining in an inward direction from a trunk-portion tip side, and convex-portion wall faces 54B inclining in a trunk-portion inward direction from a base portion side. Also, the head-portion-side engagement concave portions 44 include tip-side-concave-portion wall faces 44A inclining in a shaft-portion inward direction from a tip side, and head-portion-side-concave-portion wall faces 44C inclining in the shaft-portion inward direction from a head portion side. Then, in the condition of FIG. 9(b), if a tip portion of the pin 14 is attempted to be pushed back in a direction of being pulled out, each trunk-portion formation piece 52 can be elastically deformed smoothly in an outward direction accompanied by excellent sliding between the pin-tip-side-concave-portion wall faces 44A and the grommet-convex-portion wall faces 54A.